Coupling devices for coupling accessories to a hydraulically operated arm of excavators are well known. These devices typically are used to attach different types of attachments for example to a dipper arm of such apparatus, for example to attach different sizes of buckets or a jack hammer or other such implements to the excavator.
The coupling device (also commonly referred to as a “coupler” or “quick hitch”) is usually releasably attachable to both the (dipper) arm of an excavator and the attachment. The coupler is adapted for attachment to the arm and normally would remain on the arm and be utilised to interchangeably work different attachments on the arm. Typically, they comprise a body member which is adapted for coupling to the dipper arm, and a pair of engagement members are provided for releasably engaging a pair of spaced apart coupling pins located on the accessory. One of the engagement members typically is moveable relative to the other between an engaged state with the engagement members co-operating with each other for engaging the coupling pins of the accessory for coupling the accessory to the dipper arm, and a disengaged state for disengaging the coupling pins for releasing the accessory from the dipper arm. Typically, the moveable one of the engagement members is either slideable or pivotally carried in the body member and is moveable between the engaged and disengaged states by a ram, for example, a hydraulic ram, by a screw drive or by a linkage or lever. The engagement members most usually are formed by for example a set of hooks, typically at least two hooks. Such quick hitch couplers suffer from a number of disadvantages. In particular, where the moveable one of the two engagement members is moveable by an hydraulic ram, should the hydraulic fluid supply to the hydraulic ram fail in general, the moveable one of the engagement members returns to its disengaged state thereby releasing the accessory. This can have serious consequences, which can result in fatal accidents should the hydraulic supply to the quick hitch coupler fail when the accessory is in an elevated state with a person standing beneath it, in that the accessory could fall on the person, thus leading to fatal injuries. It will be appreciated that it is difficult for an operator to determine without leaving his cab whether the attachment is safely secured to the quick hitch coupler.
There is therefore a need for a coupler, and in particular, a quick hitch coupler for coupling an accessory to a dipper arm of a back actor which overcomes this problem.
The operation of the engagement members of the coupler are typically controlled by a hydraulic (control) ram.
A hydraulic supply from the excavator to the hydraulic control ram for the coupler is controlled by the operator of the machine operating one or more controls.
To avoid the inadvertent or accidental release of the attachment by releasing the grip of the coupler on the attachment, manually mechanical and electrically operated locking systems have been incorporated into the coupling system to ensure the attachment is only released when it is desired to do so. It is a danger that the control ram for the attachment could inadvertently be activated to release the attachment.
Mechanical locks have been provided on the coupler which require that the operator of the machine (or another person) has to manually release the mechanical lock. On the other hand in order to be effective the operator must first engage the mechanical lock—something that is not always done. Alternatively a hydraulically operated lock is provided. This lock must also be engaged by the operator.
Known electrical control systems for the release of the coupler can be operated remotely from the cab of the excavator by its operator. However there is a danger with such systems that they are accidentally operated (e.g. by accidentally hitting the remote release control) and thus release the attachment from the excavator. It will be appreciated that the release of the attachment when it is not intended to, causes a potential hazard as the attachment may fall off the coupler of the arm. If the (dipper) arm is above ground level this could potentially cause harm. In other positions the attachment might become stuck in some earth or cause damage to the dipper arm. There is thus also a need for a control system for operation of such a coupler.